Phenolic resin composition for shell molding, resin coated sand for shell molding, and shell mold formed of the same

ABSTRACT

Provided are a phenolic resin composition for shell molding that has low thermal expansion properties and high flexibility, a resin coated sand for shell molding obtained by using the same, and a shell mold formed of the same. The phenolic resin composition for shell molding that is capable of exhibiting advantageous mold characteristic is obtained by a combination of a phenolic resin that is obtained by a reaction of a phenol, a naphthol, and an aldehyde, and a fatty acid amide.

This application is a divisional of U.S. application Ser. No.13/270,524, filed Oct. 11, 2011, which is a continuation of theInternational Application No. PCT/JP2010/061591 filed on Jul. 8, 2010,which claims the benefit under 35 U.S.C. §119(a)-(d) of Japanese PatentApplication 2009-172135, filed on Jul. 23, 2009, the entireties of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a phenolic resin composition for shellmolding, a resin coated sand for shell molding, and a shell mold formedof the same. In particular, the present invention relates to a phenolicresin composition for shell molding that simultaneously solves problemsrelated to thermal expansion and flexibility, a resin coated sandobtained by using the phenolic resin composition, and a shell moldobtained by using the resin coated sand.

BACKGROUND OF THE INVENTION

Conventionally, in shell-mold casting, there is generally used a shellmold that is formed by hot-forming a resin coated sand obtained bykneading a fire-refractory particle (casting sand) and a phenolic resin(binder), and as necessary a hardener such as hexamethylenetetramine,into a desired shape. Hereinafter, the resin coated sand is referred toas “RCS”.

However, in casting process by using this kind of mold, especially byusing a mold which has a complex shape, e.g., a mold for casting amolded product such as a cylinder head of an internal combustion engine,there is a problem that a fracture or a crack (hereinafter referred toas “crack” of the mold) is easily caused on the mold during the castingprocess using the mold.

Meanwhile, it is conceivable that the crack of a mold can be preventedby lowering coefficient of thermal expansion and increasing theflexibility of mold. Patent document 1 discloses that coefficient ofrapid thermal expansion is lowered by using bisphenol such as bisphenolA and bisphenol E as a component of binder, so that low thermalexpansion properties are obtained. However, although such technique hassufficiently solved the problem of crack of the mold, the technique hasnot sufficiently solved the problem of flexibility.

Patent document 2 proposes a method in which crack of the mold isprevented by incorporating polyethylene glycol having a number averagemolecular weight of 1500 to 40000 into RCS. However, thermal expansionproperties and flexibility are not sufficiently improved by this method,and thus further improvement is needed.

Patent document 3 discloses that by using RCS formed by coating surfaceof a casting sand with a phenolic resin excellent in collapseresistance, which is produced by using at least naphthol as phenolcomponent, the improvement of regeneration rate of the used shell sandand the stability of quality of the regenerated sand can be obtainedbecause collection of a mass of shell when the mold is broken down aftermolding is improved. In examples of patent document 3, a phenolicnovolak resin and a phenolic resole resin are exemplified that areobtained by a reaction of α-naphthol, β-naphthol, or a combination ofthese naphthols, a phenol, and a formalin in the presence of a catalystsuch as hydrochloric acid and ammonia water. However, particularly inthe production of such resin by using the hydrochloric acid as acatalyst, there is a safety problem caused by vigorous reaction duringthe production of the resin, and also there is a problem of corrosion ofa die during the production of the mold. Further, patent document 3 issilent about a phenolic resin obtained by using an oxalic acid as acatalyst and RCS obtained by using the same. Furthermore, it is alsosilent about a crack of a mold which should be considered when producinga mold.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-59-178150-   Patent Document 2: JP-A-58-119433-   Patent Document 3: JP-A-63-30144

SUMMARY OF INVENTION

The present invention has been made in the light of the situationsdescribed above. It is therefore an object of the present invention toprovide: a phenolic resin composition for shell molding that has lowthermal expansion properties and high flexibility; RCS obtained by usingthe phenolic resin: a process for producing the RCS; and a shell moldobtained by using such RCS.

The inventors of the present invention have conducted intensive studyand research about the phenolic resin composition for shell molding inan effort to solve the above-described problems and found that aphenolic resin composition having effective properties can be obtainedby a combination of a phenolic resin that is obtained by a reaction ofphenol components including a phenol and a naphthol with an aldehyde,and a fatty acid amide. Specifically, they found that in the moldproduced by using RCS formed by using the above-described phenolic resincomposition, low coefficient of thermal expansion and high flexibilityare obtained. Thus, the present invention has been completed.

It is therefore a gist of the present invention to provide a phenolicresin composition for shell molding, comprising as essential components:a phenolic resin obtained by a reaction of a phenol, a naphthol, and analdehyde; and a fatty acid amide.

According to a preferable aspect of the phenolic resin composition forshell molding of the present invention, a ratio of the phenol to thenaphthol is in a range of from 95:5 to 50:50 by mass ratio.

According to another preferable aspect of the present invention, thenaphthol comprises 1-naphthol and/or 2-naphthol.

According to a further preferable aspect of the present invention, areaction molar ratio among the phenol (P), the naphthol (N), and thealdehyde (F): F/(P+N) is in a range of from 0.40 to 0.80.

According to a preferable aspect of the present invention, the fattyacid amide is present in a range of from 1 to 15 parts by mass based on100 parts by mass of the phenolic resin.

According to a favorable aspect of the present invention, the fatty acidamide is one of a monoamide, a substituted amide, and a bisamide.

According to a still further preferable aspect of the present invention,the fatty acid amide is a fatty acid bisamide, more preferably, asaturated fatty acid bisamide.

According to another favorable aspect of the present invention, thephenolic resin composition further comprises a silane coupling agent.

It is another gist of the present invention to provide RCS (resin coatedsand) for shell molding characterized in that a fire-refractory particleis coated with the phenolic resin composition for shell moldingaccording to the above aspects.

According to a preferable aspect of the RCS for shell molding of thepresent invention, the phenolic resin composition is present in a rangeof from 0.2 to 10 parts by mass based on 100 parts by mass of thefire-refractory particle.

It is a still further gist of the present invention to provide a shellmold obtained by forming and heat-curing the resin coated sand for shellmolding according to the above aspects.

It is still further gist of the present invention to provide a processfor producing a resin coated sand, comprising the steps of: (a) reactinga phenol, a naphthol, and an aldehyde in the presence of a catalyst toobtain a phenolic resin; and (b) coating a fire-refractory particle withthe phenolic resin and a fatty acid amide, which are mixed by melting,or coating a fire refractory particle with the phenolic resin and afatty acid amide, which are used independently.

According to a preferable aspect of the present invention, the catalystcomprises a divalent metal salt and/or an oxalic acid.

The phenolic resin composition for shell molding according to thepresent invention includes a phenolic resin that is obtained by areaction of a phenol, a naphthol, and an aldehyde, and a fatty acidamide. Therefore, when a coating layer including the phenolic resincomposition is formed on a surface of a predetermined fire-refractoryparticle so as to constitute RCS for shell molding and such RCS is usedto produce a shell mold, the obtained mold has low thermal expansionproperties and the flexibility of the mold can be sufficiently improved.Accordingly, a problem of casting defect of veining caused by a crack ofthe mold can be solved at the same time. In addition, since the phenolicresin can be produced without a corrosive component such as hydrochloricacid, a problem of corrosion of a die during mold-forming may not becaused. Thus, the present invention can have industrial advantages thatthe intended shell mold can be easily and safely produced.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is an explanatory view showing how the “flexibility” of mold ismeasured in examples.

DETAILED DESCRIPTION OF THE INVENTION

The phenolic resin constituting the phenolic resin composition for shellmolding of the present invention is obtained by a reaction of a phenol,a naphthol, and an aldehyde in the presence of a predetermined catalyst.

Here, examples of the phenol which is one of reaction components of aphenolic resin include conventionally known phenol, for example, phenol,alkylphenols such as cresol, xylenol, p-tert-butylphenol andnonylphenol, polyhydric phenols such as resorcinol, bisphenol F andbisphenol A, and a mixture thereof. Any one of, or any combinationthereof may be used.

The present invention is characterized by that the naphthol is used as aphenol component together with the phenol. Due to this characteristic,the properties of the phenolic resin to be obtained are effectivelyimproved. In terms of its ready availability and a reduction of cost,for example, 1-naphthol, 2-naphthol, and a mixture thereof may be usedas the naphthol. Preferably, 1-naphthol is employed because of itsexcellent reactivity with aldehyde, for example. The phenol and naphtholare employed such that the ratio of phenol to naphthol (1-naphtholand/or 2-naphthol) is in a range of from 95:5 to 50:50 by mass. In otherwords, the naphthol is employed so as to be present in an amount of 50%by mass or less, based on the total phenol component. When the amount ofthe naphthol is more than 50% by mass, an amount of generation of tarduring casting may be increased. On the other hand, when the amount ofthe naphthol is less than 5% by mass, flexibility may not besufficiently exhibited. The ratio of phenol to naphthol is preferably ina range of from 90:10 to 60:40, more preferably from 90:10 to 70:30, inview of the strength of the mold.

Examples of the aldehyde, which is reacted with the above describedphenol and naphthol to obtain the phenolic resin of the presentinvention, include formalin, paraformaldehyde, trioxan, acetaldehyde,paraldehyde, and propionaldehyde. It is to be understood that thealdehyde is not limited to the above examples, and other well-knownmaterials may be suitably used. Any one of, or any combination of thealdehyde may be used.

In the present invention, in order to obtain the intended phenolic resinby reacting the phenol (P) and the naphthol (N) with the above-describedaldehyde (F), it is recommended that the phenol and the naphthol arereacted with the aldehyde such that the blending molar ratio: F/(P+N) isin a range of 0.40 to 0.80. By controlling the blending molar ratio:F/(P+N) so as to be 0.75 or less, more preferably 0.70 or less, theflexibility can be further improved. In addition, by controlling thevalue of F/(P+N) so as to be 0.40 or more, the intended phenolic resincan be produced with a sufficient yield, and by controlling the value ofF/(P+N) so as to be 0.80 or less, the strength of the mold which isobtained by using RCS for shell molding produced by using thus obtainedphenolic resin can be advantageously improved.

In the present invention, any conventionally known catalyst such as anacid catalyst is suitably used in the reaction of the phenol and thenaphthol with the aldehyde. Especially, it is recommended that at leastone of a divalent metal salt and an oxalic acid be used as the catalyst.By using such a specific catalyst, coefficient of thermal expansion andflexibility can be further improved, and problems of metal corrosion andthe like can be advantageously solved. Examples of the divalent metalsalt include lead naphthenate, zinc naphthenate, lead acetate, zincacetate, zinc borate, lead oxide, and zinc oxide, which are metal saltshaving divalent metal element, and a combination of an acidic catalyst,which is capable of forming the metal salt, and a basic catalyst. Amongthe specific catalysts, oxalic acid is preferably used. Generally, thecatalyst including at least one selected from a group consisting of thedivalent metal salts and the oxalic acid is present in an amount of 0.01to 5 parts by mass, preferably 0.05 to 3 parts by mass, based on 100parts by mass of the total of phenol and naphthol.

The reaction of phenol, naphthol, and aldehyde in the presence of theabove-described catalyst is conducted in the same manner as aconventional production method of phenolic resin. Thus obtained phenolicresin is in a solid or a liquid (for example, varnish or emulsion) form,and expresses a heat-curing or -hardening effect when it is heated inthe presence or absence of a hardener or curing catalyst such ashexamethylene tetramine. In the present invention, a phenolic resinhaving a number average molecular weight as measured by gel permeationchromatography (GPC) in a range of from 400 to 1300 is preferably used.When the number average molecular weight of the phenolic resin is toosmall, a mold to be obtained may not have sufficient strength, becauseRCS for shell molding which is coated with the resin compositionincluding the phenolic resin has poor filling properties inmold-forming. On the other hand, when the number average molecularweight of the phenolic resin is too big, a mold to be obtained may nothave sufficient strength, because flowability of resin during heating isdeteriorated.

In the present invention, the fatty acid amide is added as an essentialcomponent to the above phenolic resin to obtain the phenolic resincomposition for shell molding. Due to the combination of the phenolicresin and the fatty acid amide, low thermal expansion properties andimproved flexibility can be advantageously achieved. The ratio of thephenolic resin to the fatty acid amid is suitably determined dependingon required properties for a mold to be obtained. Generally, 1 to 15parts by mass of the fatty acid amide is added based on 100 parts bymass of the phenolic resin. This is because, when the amount of thefatty acid amide is too small, advantages and effects to be obtained byusing the fatty acid amide may not be sufficiently exhibited. On theother hand, when the amount of the fatty acid amide is too big, theadvantages and effects that are of equal worth to the amount of thefatty acid amide may not be obtained.

Examples of the fatty acid amide, which is used in combination with thephenolic resin, include: monoamides such as saturated fatty acidmonoamide and unsaturated fatty acid monoamide; substituted amides; andbisamides such as saturated fatty acid bisamide, unsaturated fatty acidbisamide, and aromatic bisamide. Of those fatty acid amides, the fattyacid bisamide, especially, the saturated fatty acid bisamide isfavorably used.

Of the above fatty acid amide, examples of the saturated fatty acidmonoamide include lauramide, myristamide, palmitamide, stearamide, andbehenamide. Examples of the unsaturated fatty acid monoamide includeoleamide, and erucamide. Examples of the substituted amides includeN-stearyl(stearamide), N-oleyl(stearamide), N-stearyl(erucamide),methylol(stearamide), and methylol(behenamide). In addition, examples ofthe saturated fatty acid bisamide include methylenebis(stearamide),ethylenebis(stearamide), methylenebis(lauramide),methylenebis(behenamide), hexamethylenebis(stearamide),hexamethylenebishydroxyl(stearamide), N,N′-distearyl(adipamide) andethylenebis(behenamide). Examples of the unsaturated fatty acid bisamideinclude ethylenebis(oleamide), ethylenbis(erucamide),hexamethylenbis(oleamide), and N,N′-dioleyl(adipamide). Further,examples of the aromatic bisamide include xylylenebis(stearamide),xylylenebishydroxy(stearamide), and N,N′-distearyl(isophthalamide).

In the present invention, in order to use the phenolic resin and thefatty acid amide in combination for shell molding, variousconventionally known additives can be added for the purpose of improvingthe physical characteristics of the mold, for example. Examples of theadditives include silane coupling agent such asγ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.Generally, such a silane coupling agent is added in a range of fromabout 0.01 to about 5 parts by mass, preferably 0.05 to 2.5 parts bymass, based on 100 parts by mass of the phenolic resin.

In the production of RCS for shell molding according to the presentinvention, the above-described phenolic resin composition for shellmolding are kneaded into a fire-refractory particle. Because an amountof the phenolic resin composition for shell molding in RCS of thepresent invention is determined depending on a kind of resin to be usedand strength of the intended mold, for example, the amount thereof isnot necessarily limited. However, the phenolic resin composition isgenerally present in a range of from about 0.2 to about 10 parts bymass, preferably 0.5 to 8 parts by mass, more preferably 0.5 to 5 partsby mass, based on 100 parts by mass of the fire-refractory particle.

In the present invention, the kind of fire-refractory particle kneadedinto the phenolic resin composition for shell molding is notparticularly limited. As the fire-refractory particle is a basicmaterial for a mold, any known inorganic particles conventionally usedin the shell mold casting may be used as long as they have fireresistance suitable for casting and particle diameter suitable forforming a mold (mold-forming). In addition to a silica sand which iscommonly used, examples of the fire-refractory particle include, specialsands such as an olivine sand, a zircon sand, a chromite sand and analumina sand, slag particles such as a ferrochromium slag, a ferronickelslag and a converter slag, mullite-based sand particles such as NaigaiCerabeads (commercial name, available from ITOCHU CERATECH CORP.,JAPAN), and regenerated particles which are obtainable by recovering andregenerating the above particles after casting. Any one of, or anycombination of the particles may be used.

In the production of RCS for shell molding, examples of the productionmethod include, but are not limited to, any conventional methods such asa dry-hot-coating, a semi-hot-coating, a cold coating, and apowder-solvent-coating. In the present invention, a so-calleddry-hot-coating is preferably recommended that includes the steps ofkneading a preheated fire-refractory particle and a resin compositionfor shell molding in a mixer such as a whirl mixer or a speed mixer,adding aqueous hexamethylenetetramine (hardener) solution, converting anaggregated content into particles by being collapsed by cooling with anair blow, and adding a calcium stearate (lubricant). The predeterminedphenolic resin and fatty acid amide included in the resin compositionfor shell molding of the present invention can not only be melted andmixed with each other to coat the fire-refractory particle, but also canindependently be used to coat the fire-refractory particle.

Further, when making a predetermined shell mold by using theabove-described RCS for shell molding, the process for making or forminga mold by heating is not particularly limited. Any known process may beadvantageously employed. For example, a casting mold can be obtained bythe steps of: filling a forming die, which has a cavity corresponding toa shape of an intended shell mold and is heated to 150 to 300° C., withthe above-described RCS by a gravity-driven method or blowing method;curing the RCS; and removing the cured (hardened) mold from the formingdie. The mold obtained as above advantageously has the above-mentionedexcellent effect.

EXAMPLES

To further clarify the present invention, some examples of the inventionwill be described. It is to be understood that the invention is notlimited to the details of the illustrated examples and the foregoingdescription, but may be embodied with various changes, modifications andimprovements, which may occur to those skilled in the art withoutdeparting from the scope of the invention.

Here, “parts” and “%” in the following description refer to “parts bymass” and “% by mass”, respectively, unless otherwise defined. Inaddition, characteristics of the produced RCS for shell molding aremeasured in accordance with the following test methods.

—Evaluation of Flexibility of Mold—

Initially, for the evaluation of flexibility of mold, a piece of mold(120 mm×40 mm×5 mm) made of each kind of RCS was prepared under a curecondition: at 250° C. for 40 seconds. Then, the piece of mold was leftuntil it was cooled to a room temperature.

Subsequently, thus obtained piece of mold was set on a support as shownin FIG. 1, and an exothermic stick (Erema exothermic stick) wasgradually heated from 200° C. to 800° C. Meanwhile, a laser displacementgauge was positioned 10 mm away from an end portion of the piece ofmold, and data thereof was directly entered into a computer. Behaviorswith respect to the displacement were as follows: at first the piece ofmold was warped due to an expansion behavior caused by the heating ofthe piece of mold; then the piece was started to be bent; and finally,the piece of mold was fractured almost at the center thereof, i.e., atthe position heated by the exothermic stick. The term “flexibility” usedherein is expressed by the maximum deflection obtained before the pieceof mold was fractured. The higher value of the flexibility indicatesthat the mold is more easily deformed, which means that the mold isflexible. This measurement was conducted in consideration of measurementcycle such that the next measurement of a piece of mold starts when thetemperature of the exothermic stick is reached around 200° C.

—Evaluation of Coefficient of Thermal Expansion—

Evaluation of coefficient of thermal expansion was conducted inaccordance with a test method of rapid coefficient of thermal expansionspecified in JACT test method M-2, test method of coefficient of thermalexpansion. A test piece (diameter of 28.3 mm×length of 51 mm, cut intoabout ¼ of circumference) produced by heating a piece of mold at atemperature of 280° C. for 120 seconds was placed in a high-temperaturecasting sand tester controlled at 1000° C. and was taken out from itafter 1 minute. A coefficient of thermal expansion was calculated by thelengths of the test piece before the heating and after the heatingaccording to the following formula.

A coefficient of thermal expansion(%)={length of test piece(afterheating−before heating)×100}/(length of test piece before heating)

Resin Production Example 1

To a reaction vessel provided with a thermometer, a stirring device, anda condenser, 8000 parts of phenol, 2000 parts of 1-naphthol, 4106 partsof 47% formalin, and 30 parts of oxalic acid were charged. Subsequently,a temperature in the reaction vessel was gradually raised to a refluxtemperature and the mixture was subjected to a reaction under refluxcondition for 90 minutes. Further, the mixture was dehydrated underordinary pressure and heated under reduced pressure until thetemperature reached 180° C. Accordingly, unreacted phenol was removedand phenolic resin A was obtained.

Resin Production Example 2

Phenolic resin B was obtained in the same way as Resin ProductionExample 1 with the exception that 8000 parts of phenol, 2000 parts of1-naphthol, 4865 parts of 47% formalin and 30 parts of oxalic acid werecharged.

Resin Production Example 3

Phenolic resin C was obtained in the same way as Resin ProductionExample 1 with the exception that 8000 parts of phenol, 2000 parts of1-naphthol, 3159 parts of 47% formalin and 30 parts of oxalic acid werecharged.

Resin Production Example 4

Phenolic resin D was obtained in the same way as Resin ProductionExample 1 with the exception that 9000 parts of phenol, 1000 parts of1-naphthol, 4260 parts of 47% formalin and 30 parts of oxalic acid werecharged.

Resin Production Example 5

Phenolic resin E was obtained in the same way as Resin ProductionExample 1 with the exception that 6000 parts of phenol, 4000 parts of1-naphthol, 3799 parts of 47% formalin and 15 parts of oxalic acid werecharged.

Resin Production Example 6

Phenolic resin F was obtained in the same way as Resin ProductionExample 1 with the exception that 8000 parts of phenol, 2000 parts of2-naphthol, 4106 parts of 47% formalin and 30 parts of oxalic acid werecharged.

Resin Production Example 7

Phenolic resin G was obtained in the same way as Resin ProductionExample 1 with the exception that 2000 parts of phenol, 8000 parts ofbisphenol A (BPA), 2339 parts of 47% formalin and 30 parts of oxalicacid were charged.

Example 1

50 parts of ethylenebis(stearamide) and 10 parts of silane couplingagent (3-aminopropyltriethoxysilane) were mixed into 1000 parts ofphenolic resin A by heating and melting to obtain Resin composition 1.

Example 2

Resin composition 2 was obtained in the same way as Example 1 with theexception that the amount of ethylenebis(stearamide) was changed to 120parts.

Example 3

Resin composition 3 was obtained in the same way as Example 1 with theexception that the amount of ethylenebis(stearamide) was changed to 15parts.

Example 4

Resin composition 4 was obtained in the same way as Example 1 with theexception that methylenebis(stearamide) was used instead ofethylenebis(stearamide).

Example 5

Resin composition 5 was obtained in the same way as Example 1 with theexception that ethylenebis(behenamide) was used instead ofethylenebis(stearamide).

Example 6

Resin composition 6 was obtained in the same way as Example 1 with theexception that ethylenbis(erucamide) was used instead ofethylenebis(stearamide)

Example 7

Resin composition 7 was obtained in the same way as Example 1 with theexception that stearamide was used instead of ethylenebis(stearamide).

Example 8

Resin composition 8 was obtained in the same way as Example 1 with theexception that phenolic resin B was used instead of phenolic resin A.

Example 9

Resin composition 9 was obtained in the same way as Example 1 with theexception that phenolic resin C was used instead of phenolic resin A.

Example 10

Resin composition 10 was obtained in the same way as Example 1 with theexception that phenolic resin D was used instead of phenolic resin A.

Example 11

Resin composition 11 was obtained in the same way as Example 1 with theexception that phenolic resin E was used instead of phenolic resin A.

Example 12

Resin composition 12 was obtained in the same way as Example 1 with theexception that phenolic resin F was used instead of phenolic resin A.

Comparative Example 1

Resin composition 13 was obtained in the same way as Example 1 with theexception that phenolic resin G was used instead of phenolic resin A.

Comparative Example 2

Resin composition 14 was obtained in the same way as Example 1 with theexception that no fatty acid amide was added to the phenolic resin A.

Comparative Example 3

Resin composition 15 was obtained in the same way as Example 1 with theexception that no fatty acid amide was added to the phenolic resin D.

Comparative Example 4

Resin composition 16 was obtained in the same way as Example 1 with theexception that no fatty acid amide was added to the phenolic resin E.

Comparative Example 5

Resin composition 17 was obtained in the same way as Example 1 with theexception that no fatty acid amide was added to the phenolic resin F.

Production Example 1 of RCS

To a laboratory whirl mixer, 7000 parts of fire-refractory particle(regenerated silica sand) heated to 130 to 140° C. and 105 parts of thephenolic resin composition obtained in each of the above Examples 1 to12 and Comparative Examples 1 to 5, were added and kneaded for 60seconds. Then, after 23 parts of hexamethylenetetramine dissolved in 105parts of water was added thereto and cooled by an air blow, 7 parts ofcalcium stearate was added. As a result, RCS for shell molding (Samples1 to 17) produced by using each of the resin compositions of the aboveExamples and Comparative Examples were obtained.

Production Example 2 of RCS

To a laboratory whirl mixer, 7000 parts of fire-refractory particle(regenerated silica sand) heated to 130 to 140° C., and 105 parts of theabove phenolic resin A and 5.25 parts of ethylenebis(stearamide), whichconstitute Resin composition 18, were each independently added andkneaded for 60 seconds. Then, after 23 parts of hexamethylenetetraminedissolved in 105 parts of water was added thereto and cooled by an airblow, 7 parts of calcium stearate was added. As a result, RCS for shellmolding (Sample 18) was obtained.

EVALUATION

In accordance with the test method described above, each RCS (Samples 1to 18) obtained as above was subjected to the measurement of flexibilityand coefficient of thermal expansion of mold. The results thereof areshown in the following Table 1 and Table 2, together with the productioncondition of phenolic resin.

TABLE 1 RCS Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample7 Sample 8 Sample 9 Resin composition 1 2 3 4 5 6 7 8 9 ComponentsPhenolic resin A A A A A A A B C Phenol [%] 80 80 80 80 80 80 80 80 801-naphthol [%] 20 20 20 20 20 20 20 20 20 2-naphthol [%] — — — — — — — —— BPA [%] — — — — — — — — — Molar Ratio 0.65 0.65 0.65 0.65 0.65 0.650.65 0.77 0.50 F/(P + N) Fatty acid amide Ethylenebis Methyl-Ethylenebis Ethylenebis Stearamide Ethylenebis (stearamide) enebis(behen- (erucamide) (stearamide) (stearamide) amide) Amount [part] 5 121.5 5 5 5 5 5 5 (based on 100 parts by mass of resin) Mold coefficient0.73 0.72 0.75 0.74 0.72 0.72 0.71 0.69 0.77 characteristics of thermalexpansion [%] flexibility 7.2 10.0 5.8 7.5 7.1 7.4 7.8 5.4 9.8 [mm]

TABLE 2 RCS Sample 10 Sample 11 Sample 12 Sample 13 Sample 14 Sample 15Sample 16 Sample 17 Sample 18 Resin Composition 10 11 12 13 14 15 16 1718 Components Phenolic resin D E F G A D E F A Phenol [%] 90 60 80 20 8090 60 80 80 1-naphthol [%] 10 40 — — 20 10 40 — 20 2-naphthol [%] — — 20— — — — 20 — BPA [%] — — — 80 — — — — — Molar Ratio 0.65 0.65 0.65 0.650.65 0.65 0.65 0.65 0.65 F/(P + N) Fatty acid amide Ethylenebis(stearamide) — Ethylenebis (stearamide) Amount [parts] 5 5 5 5 0 0 0 0 5(based on 100 parts by mass of resin) Mold coefficient of thermal 0.750.71 0.76 0.73 0.76 0.77 0.74 0.78 0.74 characteristics expansion [%]flexibility [mm] 6.3 10.5 8.4 3.9 4 2.9 3.4 3.1 7.0

As apparent from the results shown in Table 1 and Table 2, every RCS(Samples 1 to 12) obtained by using the resin compositions 1 to 12 whichinclude phenolic resins A to F of Resin production examples 1 to 6 and apredetermined fatty acid amide, which are in accordance with the presentinvention, has low coefficient of thermal expansion and highflexibility. On the other hand, RCS (Sample 13) obtained by using thephenolic resin G of Resin production example 7, in which phenol andbisphenol A was used as the phenol components, has low flexibility.Further, RCS (Samples 14 to 17) obtained by using the resin compositions14 to 17, in which no fatty acid amide was added to phenolic resin A, D,E and F, have low flexibility. Furthermore, RCS (Sample 18) obtained byindependently adding the phenolic resin A and the fatty acid amide,which constitute a resin composition, into a fire-refractory particlehas excellent low coefficient of thermal expansion and excellentflexibility.

What is claimed is:
 1. A resin coated sand for shell molding, wherein afire-refractory particle is coated with a phenolic resin compositioncomprising a resin consisting of a phenolic resin obtained by a reactionof a phenol, a naphthol, and an aldehyde; and a fatty acid amide.
 2. Theresin coated sand for shell molding according to claim 1, wherein aratio of the phenol to the naphthol is in a range of from 95:5 to 50:50by mass ratio.
 3. The resin coated sand for shell molding according toclaim 1, wherein a ratio of the phenol to the naphthol is in a range offrom 90:10 to 60:40 by mass ratio.
 4. The resin coated sand for shellmolding according to claim 1, wherein the naphthol comprises at leastone of 1-naphthol and 2-naphthol.
 5. The resin coated sand for shellmolding according to claim 1, wherein a reaction molar ratio among thephenol (P), the naphthol (N), and the aldehyde (F): F/(P+N) is in arange of from 0.40 to 0.80.
 6. The resin coated sand for shell moldingaccording to claim 1, wherein the fatty acid amide is present in a rangeof from 1 to 15 parts by mass based on 100 parts by mass of the phenolicresin.
 7. The resin coated sand for shell molding according to claim 1,wherein the fatty acid amide is one of a monoamide, a substituted amide,and a bisamide.
 8. The resin coated sand for shell molding according toclaim 1, wherein the fatty acid amide is a fatty acid bisamide.
 9. Theresin coated sand for shell molding according to claim 8, wherein thefatty acid bisamide is a saturated fatty acid bisamide.
 10. The resincoated sand for shell molding according to claim 1, wherein the phenolicresin composition further comprises a silane coupling agent.
 11. Theresin coated sand for shell molding according to claim 1, wherein thephenolic resin composition is present in a range of from 0.2 to 10 partsby mass based on 100 parts by mass of the fire-refractory particle. 12.The resin coated sand for shell molding according to claim 1, wherein amold produced by using the resin coated sand has a flexibility of atleast 5.4 mm.
 13. The resin coated sand for shell molding according toclaim 1, wherein the phenolic resin is obtained by a reaction of phenol,naphthol and an aldehyde in the presence of an acid catalyst.
 14. Ashell mold obtained by forming and heat-curing the resin coated sand forshell molding according to claim 1.